It was hypothesized that herbivores regulate periphyton succession in acidified lakes by suppressing loosely attached filamentous algae that otherwise persist and outcompete other growth forms for resources, such as dissolved inorganic carbon (DIC). This hypothesis was tested by conducting grazer-exclosure experiments over an ice-free season in acidified and circumneutral lakes that differed in DIC concentrations. In each lake, the two-factor experimental design had two herbivore (presence-absence) and five succession (early-late) treatments. Total periphyton biomass was greater and significantly suppressed by herbivores in the circumneutral lake. Here, acid-sensitive green frog (Rana clamitans) tadpoles suppressed loosely attached (i.e., zygnematacean taxa) while stimulating firmly attached (i.e., Coleochaete scutata) algae, causing succession towards a herbivore-resistant physiognomy. Conversely, a loosely attached and tall physiognomy persisted in the absence of significant grazing and greater resource limitation in the acid lake. Our findings suggest that trade-offs between competitiveness and herbivore resistance help predict changes in periphyton in recovering acidified lakes. During recovery, concomitant increases in herbivory and resources should favour a firmly attached and short periphyton physiognomy that is resistant to removal by herbivores, but that lacks the competitiveness of loosely attached and tall forms in DIC-limited acid lakes.